The present invention relates to a commercially feasible process for preparing alkyl nitroacetates. More particularly, it relates to a process for preparing alkyl nitroacetates by reacting a nitroparaffin with a cyanoformate in the liquid phase.
Alkyl nitroacetates are useful compounds for preparing alpha-nitrocarboxylic acids by reacting the same with alkyl halide, aldehyde, tertiary amines, and the like. It is also well known that production of amino acids such as phenyl alanine, dopa, methyl dopa, tryptophan, alpha-methyltryptophan, etc. is easily carried out by hydrogenating alpha-nitrocarboxylic acids.
Various processes for preparing alkyl nitroacetates are known. For example, (1) Kornblum et al. reported in J. Am. Chem. Soc., 77, 6654 (1955) that ethyl nitroacetates were obtained by reacting ethyl iodoacetate with silver nitrite; (2) Kinkseiner and his coworkers reported in J. Org. Chem., 28, 215 (1963) that a magnesium complex of nitroacetic acid was obtained by reacting nitromethane with methyl carbonate magnesium, which was, then subjected to esterification to obtain nitroacetic acid ester using a strong acid; (3) Zen et al. reported in J. Chem. Soc. of Japan, Ind. Chem. Sec., 74, 70 (1971) that methazonic acid salt was obtained by reacting 2 moles of nitromethane with 8 moles of potassium hydroxide, which was then esterified to obtain a nitroacetic acid ester using a strong acid; (4) Sifniades and others disclosed in J. Org. Chem., 40, 3562 (1975) that a nitroacetoacetic acid ester was obtained by reacting an acetoacetic acid ester with an acyl nitrate, which was then decomposed with an alcohol to obtain a nitroacetic acid ester and (5) Honda et al., in U.S. Pat. No. 4,495,362, disclose that alkyl nitroacetates can be formed by reacting a nitroparaffin with an alkyl phenyl carbonate.
Among the processes mentioned above, processes (1) and (2) are not practical as they involve the use of expensive silver salt or magnesium metal as starting materials. Process (3) is not feasible on a large scale application as the reaction requires heating of alkali metal salts of nitromethane which presents the possibility of a dangerous detonation. Process (4) necessitates the use of relatively expensive materials, such as acetoacetic acid ester and acyl nitrates while process (5) requires the use of alkyl phenyl carbonate, a material which is not commercially available, is formed from phosgene and, thereby, presents a handling and safety problem and which, when formed, requires a difficult separation from the product mixture which includes the dialkyl and diphenyl derivatives as well.